According to the documentation, MapThread works on Association objects. But it doesn't seem to evaluate the passed function. For example:

MapThread[#1 + #2 &, {<|a -> 1, b -> 2|>, <|a -> 5, b -> 6|>}]

returns:

<|a -> (#1 + #2 &)[1, 5], b -> (#1 + #2 &)[2, 6]|>

I would have expected <| a -> 6, b -> 8 |>.